1. Field of the Invention
The present invention is a surgical device. More specifically, the present invention relates to a tissue ablation device assembly with an irrigated ablation member which is adapted to produce a lesion within tissue. The present invention also relates to the construction of the ablation member.
2. Description of Related Art
Cardiac arrhythmias, and atrial fibrillation in particular, remain a persistent medical condition in modern society. Persistence of atrial fibrillation has been observed to cause or at least contribute to various medical conditions including congestive heart failure, stroke, other thromboembolic events, and myocardial ischemia.
Several surgical approaches have been developed for the purpose of treating or preventing cardiac arrhythmias, and in particular more recently with the intention of treating atrial fibrillation. One such example, known as the “maze procedure”, is disclosed by Cox, J L et al. in “The surgical treatment of atrial fibrillation I. Summary” Thoracic and Cardiovascular Surgery 101(3), pp. 402-405 (1991); and also by Cox, J L in “The surgical treatment of atrial fibrillation. IV, Surgical Technique”, Thoracic and Cardiovascular Surgery 101(4), pp. 584-592 (1991). In general, the “maze” procedure is designed to relieve atrial arrhythmia by restoring effective atrial systole and sinus node control through a prescribed pattern of incisions about the cardiac tissue wall. In the early reported clinical experiences, the “maze” procedure included surgical incisions in both the right and the left atrial chambers. However, more recent reports predict that the surgical “maze” procedure may be substantially efficacious when performed only in the left atrium, such as is disclosed in Sueda et al., “Simple Left Atrial Procedure for Chronic Atrial Fibrillation Associated With Mitral Valve Disease” (1996).
The “maze procedure” as performed in the left atrium generally includes forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the inferior pulmonary veins en route. An additional horizontal line also connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the precipitating conduction to the atrial arrhythmia by creating conduction blocks within the aberrant electrical conduction pathways.
While surgical intervention such as the “maze” procedure has been moderately successful in treating atrial arrhythmia, this highly invasive methodology is believed to be prohibitive in many cases. However, these procedures have provided the principle that electrically isolating faulty cardiac tissue may successfully prevent atrial arrhythmia, and particularly atrial fibrillation caused by perpetually wandering reentrant wavelets or focal regions of arrhythmogenic conduction. Hence the development of less invasive catheter-based approaches to treat atrial fibrillation through cardiac tissue ablation intended to emulate the maze-type procedures.
In general, known catheter-based therapies for cardiac arrhythmias involve introducing a catheter within a cardiac chamber, such as in a percutaneous translumenal procedure, such that an energy sink on the catheter's distal end portion is positioned at or adjacent to the aberrantly conductive tissue. The energy sink is activated according to various known modes of operation such that the targeted tissue adjacent thereto is ablated and rendered non-conductive as to the propagation of cardiac rhythm.
One particular type of energy sink which has been disclosed for use as an ablation element is a heat sink which ablates tissue by use of thermal conduction, for example by means of a resistive wire which heats upon application of a current in a closed loop system within an ablation catheter. A threshold temperature that has been disclosed for ablating tissue according to a thermal conduction mode of ablation is generally above 45 degrees C. usually from 45 to 70 degrees C., typically 50 to 65 degrees C., and preferably from about 53 to 60 degrees C. It has also been observed that high temperatures, such as temperatures above 70 degrees C., may produce charring at the tissue-ablation element interface, It has been further observed that such charring may cause adverse medical results such as thrombosis on the tissue wall in the case of tissue ablation of the cardiac chambers including the atrium.
Another previously disclosed energy sink for use as an ablation element includes an electrode which emits direct current (DC), such as from an electrode on the distal end of a catheter placed adjacent to the targeted tissue and coupled by way of the body's own conductivity to a return electrode. However, more modern current-based ablation elements which have been disclosed for use in tissue ablation devices and procedures instead use radio frequency (RF) current driven electrodes. According to RF electrode ablation, the electrode is placed adjacent to the target tissue and is electrically coupled to a return electrode that may be provided on the same or another invasive device, or more generally is provided as a large surface area conductive patch provided on the patient. Current flowing between the electrode and the patch is at its highest density at the tissue location adjacent to the treatment electrode, and therefore causes ablation of the tissue. It is believed that this arrangement is adapted to ablate tissue both by way of thermal conduction at the electrode-tissue interface, in addition to thermal ablation caused by resistive or dielectric heating of the tissue itself as it resides in the high current density region of the RF current path.
In addition to the energy sinks just described for use as tissue ablation elements, other energy sources which have been disclosed for use in catheter-based ablation procedures include microwave energy sources, cryoblation energy sources, light energy sources, and ultrasound energy sources.
Various specific catheter-based tissue ablation devices and methods have also been disclosed for forming lesions of specific geometry or patterns in the target tissue. In particular, various known tissue ablation devices have been adapted to form either focal or linear (including curvilinear) lesions in the wall tissue which defines the atrial chambers.
Less-invasive percutaneous catheter ablation devices and techniques have been disclosed which use variations of “end-electrode” catheter designs for delivering a point source of energy to ablate the area of abnormal electrical activity, such as where atrial fibrillation is believed to be focal in nature, one example of abnormal electrical activity is where a focal arrhythmia originates from a pulmonary vein of the left atrium. The end electrodes form localized lesions that ablate the focus, thus ablating and thereby treating such focal arrhythmias in the pulmonary veins. Examples of previously disclosed therapeutic focal ablation procedures for ablating foci in the pulmonary vein may be found in the following references: “Right and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation”, Haissaguerre et al., Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996); and “A focal source of atrial fibrillation treated by discrete radiofrequency ablation”, Jais et al., Circulation 95:572-576 (1997).
Focal tissue ablation, however, is not generally believed to be appropriate for many cases of atrial fibrillation of the “multi-wavelet” type which involve multiple reentrant loops which are believed to arise from various arrhythmogenic sources. These multiple excitation waves would simply circumnavigate a focal ablative lesion within the cardiac tissue. Therefore, similar to the surgical “maze” procedure described above, continuous linear lesions are believed to be necessary in order to completely segment the atrial tissue so as to block the wave fronts associated with most forms of atrial fibrillation. Therefore, other specific tissue ablation devices have also been disclosed which are adapted to make linear lesions for the particular purpose of treating and preventing this multi-wavelet form of atrial fibrillation.
Various tissue ablation device assemblies and methods of use have been disclosed for making linear lesions with a single distal electrode tip adapted to either drag or form sequential point lesions along a tissue wall, herein referred to as “drag” assemblies and procedures. According to one disclosed form of a true drag procedure, as the RF energy is being applied, the catheter tip is drawn across the tissue along a predetermined pathway within the heart. Alternatively, lines of ablation using distal tip electrode catheter assemblies can be made by sequential positioning and ablation along the pathway,
In one particular example intended to use single point electrode catheter assemblies to form linear lesions in a maze-type procedure, shaped guiding sheaths are used to position an end electrode on a deflectable or shaped catheter along a predetermined path of tissue to be ablated. According to this disclosed assembly and method, a continual, transmural lesion must be made by remote, percutaneous manipulation of the device using only the means of X-ray fluoroscopy for visualizing catheter location in the beating cardiac chamber. Moreover, it has been observed that this process may fail to produce continuous, transmural lesions, thus leaving the opportunity for the reentrant circuits to reappear in the gaps remaining between point or drag ablations.
Further more detailed examples of tissue ablation device assemblies which use sequential application of energy from a point on a catheter which is remotely manipulated to ostensibly create an ablation maze according to a predetermined pattern, such as according to the examples just described, are disclosed in the following references: U.S. Pat. No. 5,427,119 to Swartz et al.; U.S. Pat. No. 5,564,440 to Swanz et al.; U.S. Pat. No. 5,515,166 to Swartz et al.; and U.S. Pat. No. 5,690,611 to Swartz et al.
In addition to the “drag” type procedures described above using end electrode catheters to form linear lesions, other assemblies have been disclosed which provide multiple electrodes along a length of the distal end portion of a catheter in order to form lines of conduction block along cardiac chamber wall tissue adjacent to the multi-electrode segment. These catheter assemblies generally include a plurality of ring or coil electrodes circling the catheter at spaced intervals extending proximally from the distal tip of the catheter.
According to several disclosed examples of “multi-electrode” tissue ablation devices of this type (and also further according to various designs of the “end-electrode” type), a catheter upon which a linear electrode array is positioned is provided with a steerable tip. These catheters generally include one or more steering wires, extending from a steering mechanism at the proximal end of the catheter to an anchor point at the distal end of the catheter. By applying tension to the steering wire or wires, the tip of the catheter can be deflected at least along one plane which at least in-part allows the catheter's distal end with electrodes to be steered to a desired direction. Furthermore, at least one other known tissue ablation catheter comprise a rotatable steering feature which allows the distal end of the catheter to be rotated about its longitudinal axis by manipulating the proximal end of the catheter. Once the catheter is steered and positioned against a predetermined region of body tissue within a body chamber according to these various disclosed assemblies, ablating elements may be activated to form a lesion.
Tissue ablation device assemblies have also been designed wherein a catheter having a predetermined curve is received within a sheath that is advanced over the distal end of the catheter. Advancement of the catheter within the sheath modifies the predetermined curve of the distal end of the catheter. By inserting different shaped guide catheters through the outer guide catheter, different shapes for the distal end of the catheter are created. Other disclosed linear lesion assemblies include preshaped catheters with electrodes along the shaped portion, including “hairpins” or “J-shapes”.
More detailed examples of catheter-based tissue ablation devices and methods for forming long linear lesions in tissue along the walls of the atrial chambers, such as according to at least some of the examples just described, are disclosed in the following disclosure: U.S. Pat. No. 5,545,193 to Fleischman et al.; U.S. Pat. No. 5,549,661 to Kordis et al.; U.S. Pat. No. 5,617,854 to Munsif; PCT Publication WO 94/21165 to Kordis et al.; and PCT Publication WO 96/26675 to Klein et al. The disclosures of these references are herein incorporated in their entirety by reference thereto.
During tissue ablation procedures, and particularly of the RF ablation type, it is critical to maintain precise positioning and contact pressure of the ablation electrode or electrodes against the cardiac tissue to create a continuous, linear lesion to properly treat the arrhythmic condition. Therefore, more recently disclosed catheter-based cardiac tissue ablation assemblies and methods are adapted to include more complex mechanisms for manipulating and positioning the ablation element precisely and securely at desired locations in a cardiac chamber and also for forming particularly desired lesion patterns in such chambers. Previously disclosed catheters of this type include: a three dimensional basket structure with single or multiple electrodes which are moveable along a plurality of spines which are intended to be held in place along tissue by means of the expanded basket in the atrium; a device having flexible electrode segments with an adjustable coil length which may form a convoluted lesion pattern with varying length; a composite structure which may be variously flexed along its length to form a variety of curvilinear shapes from a generally linear shape; proximally constrained diverging splines which expanded upon emergence from an opening in the distal end of an elongated catheter and having a multi-electrode element extending therebetween; a probe device having an ablation element which is adapted to bend or bow outwardly of the probe and against a desired region of tissue; and a device having an outer delivery sheath and an elongated electrode device slideably disposed within the inner lumen of the delivery sheath such that proximal manipulation of the electrode device causes its distal multi-electrode section to arch or “bow” outwardly away from the distal section of the delivery sheath.
More detailed examples of catheter-based tissue ablation assemblies and methods for creating long linear lesions in cardiac tissue, such as according to the types just described, are variously disclosed in the following references: U.S. Pat. No. 5,592,609 to Swanson et al.; U.S. Pat. No. 5,575,810 to Swanson et al.; PCT Published Application WO 96/10961 to Fleischman et al.; U.S. Pat. No. 5,487,385 to Avitall; U.S. Pat. No. 5,702,438 to Avitall; U.S. Pat. No. 5,687,723 to Avitall; and PCT Published Application WO 97/37607 to Schaer. The disclosures of these references are herein incorporated in their entirety by reference thereto.
In addition to those known assemblies just summarized above, additional tissue ablation device assemblies have also been recently developed for the specific purpose of ensuring firm contact and consistent positioning of a linear ablation element along a length of tissue by anchoring the element at least at one predetermined location along that length, such as in order to form a “maze”-type lesion pattern in the left atrium. One example of such assemblies includes an anchor at each of two ends of a linear ablation element in order to secure those ends to each of two predetermined locations along a left atrial wall, such as at two adjacent pulmonary veins, so that tissue may be ablated along the length of tissue extending therebetween.
Fluid Irrigated Ablation Elements
In addition to the various catheter and ablation element features just described above according to various known tissue ablation device assemblies, other assemblies have also disclosed a means for coupling an ablation element to a controlled flow of fluid for the purpose of enhancing the ablative response of tissue at the tissue-ablation element interface. The resulting ablation elements are referred to as “fluid irrigated” ablation elements or electrodes.
For example, one previously disclosed tissue ablation device which is intended for thermal ablation of hollow body organs (disclosed examples include gallbladder, the appendix, the uterus, the kidney) or hollow body passages (disclosed examples include blood vessels, and fistulas) by heating such tissues provides a managed flow of thermally conductive fluid medium flows across a resistive heating wire disposed over a catheter body. The thermally conductive fluid medium is intended to enhance and provide uniformity of heat transfer from the resistance heater coil, and is provided to the heater coil at a temperature from 37 to 45 degrees C. in order to shorten the time necessary to raise the temperature of the medium to the treatment temperature. In one particular disclosed variation of this assembly and method, the fluid flows from a tube and through apertures between turns of the wire disposed over the tube. In another disclosed variation of this example, the fluid flows through a heating element, which may be a perforated or permeable structure such as a wire mesh or other perforated cylindrical structure. In still a further disclosed variation, the fluid medium flow oscillates, where volume of the fluid is alternatively infused and aspirated from the region of the heater coil in order to control temperature in that region.
More detailed examples of tissue ablation device assemblies and methods which couple thermally conductive fluid medium to a resistive heating element for the purpose of enhancing heat transfer to tissue is disclosed in U.S. Pat. No. 5,433,708 to Nichols et al.
Other previously disclosed tissue ablation devices, in particular ablation devices of the RF electrode variety, are also adapted to couple fluid to the tissue-ablation element interface, such as for the intended purpose of cooling the tissue during RF ablation, due at least in-part to the narrow ranges of acceptable tissue temperatures for such ablation as described previously above. According to this intended fluid cooling function, various other means have also been disclosed for controlling the temperature at the tissue-ablation element interface during ablation, for example including assemblies using feedback control of the amount of energy or current flowing to and from the ablation element based upon measured temperature or impedance at the tissue interface. In addition, another intended result for previously disclosed fluid irrigated RF electrode assemblies, particularly those of the multi-electrode type for forming linear maze-type lesions such as described above, is to evenly distribute the current density flowing into the tissue along the length of the RF ablation element.
For example, several previously disclosed fluid-coupled RF ablation assemblies and methods use fluid to cool an electrode element during RF ablation by circulating the fluid internally through the catheter, including through a chamber formed by an inner surface or backing of the electrode. Such assemblies intend to cool the tissue-electrode interface by cooling the electrode itself during ablation, and include those of the “end-electrode” type, further including such assemblies of the deflectable tip/steerable variety, in addition to assemblies adapted with larger surface ablation elements for forming large lesions, such as for making linear lesions in maze-type procedures. In one further disclosed example, a passive heat conduction means is coupled to the interior of an end electrode and is made up of a fibrous material such as cotton fibers which have been impregnated with a heat absorbing fluid such as saline or water. As the end electrode heats during ablation, the temperature is conducted away from the electrode, into the passive heat conduction means where it is dissipated toward a cooler portion.
Other disclosed variations of fluid cooled RF ablation assemblies include ports through which the cooling fluid may flow outwardly from the catheter to enhance the cooling thermal transfer from the electrode to the fluid. In one known example of this type, the fluid flows through apertures in the ablation catheter adjacent to the electrode, and in alternatively disclosed variations fluid flows through apertures in the electrode itself. In another previously disclosed tissue ablation assembly of the end-electrode type, a plurality of lumens include distal ports adjacent to the end electrode and are adapted to allow cooling fluid to flow over the exterior surface of the electrode adjacent to the tissue-electrode interface at the electrode's tip.
Other examples of known tissue ablation device assemblies using fluid irrigated electrodes are instead adapted to provide fluid irrigation directly to the tissue-electrode interface. In one known example of this type, apertures are formed in a metallic end-electrode at its distal arcuate surface or tip where the electrode is intended to contact the target tissue. This assembly is intended to provide a path for internally circulating fluid within the chamber formed by the end electrode to flow into the tissue-electrode interface during ablation.
Another example of a tissue ablation device intended to ablate an inner layer of an organ in the body, and more particularly the endometrium, includes an inflatable member with an interior that houses an electrolytic solution such as saline. The balloon has a back side, and a front side that includes a plurality of apertures. The electrolytic solution is permitted to selectively flow from the interior through the apertures at a flow rate that is dependent on the pressure applied to the balloon by the electrolytic solution. A conforming member includes a conductive surface and a back side oriented toward the perforate front side of the balloon. The conforming member is further disclosed to be between 0.01 and 2.0 centimeters thick, and may be made of an open cell foam or thermoplastic film material, such as silicon reinforced natural gum rubber, neoprene, soft gum rubber, and polyurethane material, which is adapted to conform to the irregular inner surface the endometrium. The disclosed construction for the conductive surface of the conforming member includes extruded conductive materials forming the member itself, implanted conductive ions onto the member, or a conductive surface coating such as in the form of a printed circuit. According to one further disclosed optional embodiment of this assembly, a relatively strong membrane may be positioned between the balloon and the conforming member and passes the electrolytic fluid from the balloon to the conforming member. The optional membrane is further disclosed to be made of a microporous material such as mylar, expanded PFT such as Gortex available from Gore Company.
According to the disclosed method of use for this assembly, the back side of the balloon presses against the interior of the uterus. As pressure within the balloon increases with electrolytic fluid, the conforming member confronts the opposite wall of the endometrium. The combination of the conforming member and the application of electrolytic solution through the conforming member is further disclosed to provide for the effective delivery of RF energy to the endometrium.
In a further disclosed variation of the endometrial ablation device assembly just described, a balloon having a plurality of apertures through its outer skin has a particular shape when expanded which approximates that of the inter-uterine space. A conforming member similar to the type just described for the previous assembly is provided substantially around the outer surface of the balloon and is further adapted to be compressible to thereby conform to the endometrium. A printed circuit is provided as an ablation element and can be formed in or on the conforming member, or adjacent to its backside or conductive surface and delivers RF energy to selected sections of the endometrium. Fluid flows through the apertures in the balloon, through the foam-like conforming member, and into the endometrium during ablation. An optional porous membrane is further disclosed which is positioned between the conforming member and the balloon.
Various additional variations of the endometrial ablation assemblies just described have also been disclosed. In one such disclosure, the expandable member which forms the balloon may be made of a microporous material that does not include distinct apertures. Further disclosed compositions for the foam-like conforming member to adapt it to be moldable and formable to irregular surfaces of the endometrium include knitted polyester, continuous filament polyester, polyester-cellulose, rayon, polyimide, polyurethane, polyethylene. In still a further disclosed embodiment, zones of lower porosity may be created along the outer surface of the device by sealing two conforming members together about an electrode in order to retain electrolytic solution at the electrode to elevate the temperature there and create a larger ablative electrode effect. In one more detailed disclosure of this configuration, two pieces of UltraSorb foam were sealed between 0.004 inch by 0.016 inch flat electrode wire with about 1.0 inch of SST wire exposed in the foam. Various further disclosed foam sizes of this variety include thicknesses of: (i) 1/16 inch by ⅛ inch, (ii) ⅛ inch by 1/16 inch; and (iii) 1/16 inch by 1/16 inch, wherein the foam size was about 1.0 inch by 1.0 inch.
Another example of a known fluid irrigated tissue ablation electrode device assembly intended for use in creating a linear lesion in a maze-type procedure in the atrium includes a fluid irrigated linear lesion electrode element on a catheter having a removable preshaped stylet intended to conform the region of the ablation element to the inner surface of the atrium. A foam layer formed of open cell polyurethane, cotton-like material, open-cell sponge, or hydrogels is disposed over the electrode element and is permeable by conductive fluids and exhibits some compressibility. The foam layer is enclosed within a fluid impermeable covering which includes a plurality of tiny holes intended to help focus the RF energy onto the target tissue within the heart. The covering is formed of heat shrink polyethylene, silicone, or other polymeric material comprised of conduction wires or flat conductive ribbons which are insulated but stripped of the insulation at spaced intervals along the ablation section. Conductive fluid flows over the electrode element through a lumen in the catheter shaft, through holes in the catheter shaft, to the compressible foam layer, and through the perforated covering during ablation. The electrode element according to this variation is formed of a conductive wire or flat ribbon extending along the lumen with selected insulated and non-insulated portions.
Still a further known tissue ablation device assembly which is intended to form linear maze-type lesions in an atrium includes the use of fluid irrigated electrodes along a loop which is adapted to be positioned within the heart such that the ablation section on one side of the loop is leveraged against a chamber wall by action of the opposite side of the loop against an opposing chamber wall. A plurality of electrodes are positioned over an infusion tube with holes. A compressible foam layer is positioned over the electrodes and is covered by a covering which is perforated with discrete holes. Fluid flows from the infusion tube, through the holes in the tube and past the energized electrodes, through the foam layer, and finally outward through the holes in the outer covering during ablation. A conductive fluid such as conductive saline may be used in a manner to create a conductive path between the electrodes and the target tissue, and also to cool the ablation electrodes.
Other more detailed examples of ablation devices which flow fluid between electrodes and tissue when current is flowing from the electrodes to the tissue, such as according to the examples just described, are disclosed in the following references: U.S. Pat. No. 5,348,554 to Imran et al.; U.S. Pat. No. 5,423,811 to Imran et al; U.S. Pat. No. 5,505,730 to Edwards; U.S. Pat. No. 5,545,161 to Imran et al.; U.S. Pat. No. 5,558,672 to Edwards et al.; U.S. Pat. No. 5,569,241 to Edwards; U.S. Pat. No. 5,515,788 to Baker et al.; U.S. Pat. No. 5,658,278 to Imran et al.; U.S. Pat. No. 5,688,267 to Partescu et al.; U.S. Pat. No. 5,697,927 to Imran et al.; PCT Patent Application Publication No. WO 97/32525 to Pomeranz et al.; and PCT Patent Application Publication No. WO 98/02201 to Pomeranz et al.
None of the cited references disclose a tissue ablation member having an ablation element with a length that is covered and enclosed by a single, thin layer of a porous fluid-permeable membrane which is adapted to communicate with a pressurizable fluid source in order to irrigate the tissue-ablation element interface with fluid from that fluid source in an even manner along the ablation element length.
Nor do the cited references disclose a tubular member with a distal fluid permeable portion that is adapted to slideably receive a tissue ablation device such that an ablation element along the ablation device is positioned within the fluid permeable portion so a conductive fluid may be infused over the ablation device within the tube, over the ablation element, and outwardly through the permeable portion and into a tissue-ablation element interface along the fluid permeable portion.